A silicon epitaxial wafer is manufactured as follows, for example.
That is, in a state that a silicon single crystal substrate is placed in a reaction vessel of a vapor-phase growth apparatus and a hydrogen gas is flowed, a temperature in the reaction vessel is increased to 1100° C. to 1200° C. (a temperature increasing step).
Further, when the temperature in the reaction vessel reaches 1100° C. or above, a natural oxide film (SiO2: Silicon Dioxide) formed on a substrate surface is removed.
In this state, a silicon source gas such as trichlorosilane (SiHCl3) and a dopant gas such as diborane (B2H6) or phosphine (PH3) are supplied into the reaction vessel together with the hydrogen gas. In this manner, a silicon single crystal thin film is vapor-phase grown on a main surface of the substrate (a film forming step).
After vapor-phase growing the thin film in this manner, the supply of the source gas and the dopant gas is stopped, and the temperature in the reaction vessel is reduced while maintaining a hydrogen atmosphere (a cooling step).
When a heavy-metal impurity is mixed into an epitaxial layer (the silicon single crystal thin film) during the process for manufacturing a silicon epitaxial wafer as described above, characteristics of a device fabricated using this substrate may become abnormal in some cases.
When a surface layer side of the epitaxial layer that serves as a device active layer on which a device is formed is contaminated with an impurity, the device is considerably adversely affected.
As a conventional method for reducing heavy-metal impurity concentration in a silicon epitaxial wafer, for example, there has been disclosed a method for switching an atmospheric gas from a hydrogen atmosphere to a nitrogen atmosphere at 400° C. or below to precipitate Cu on a surface of the wafer at a cooling step of manufacture of a silicon epitaxial wafer and then removing a surface layer or a manufacturing method for switching an atmospheric gas from a hydrogen atmosphere to a nitrogen atmosphere at a temperature higher than 400° C. to precipitate Cu in a bulk portion rather than the surface so that the precipitation can be avoided in the surface layer portion (see Patent Document 1).